Sets the etag, last_modified, or both on the
response and renders a 304 Not Modified response if the
request is already fresh.

Parameters:

:etag Sets a “weak” ETag validator on the response. See the
:weak_etag option.

:weak_etag Sets a “weak” ETag validator on the response.
Requests that set If-None-Match header may return a 304 Not Modified
response if it matches the ETag exactly. A weak ETag indicates semantic
equivalence, not byte-for-byte equality, so they're good for caching
HTML pages in browser caches. They can't be used for responses that
must be byte-identical, like serving Range
requests within a PDF file.

:strong_etag Sets a “strong” ETag validator on the response.
Requests that set If-None-Match header may return a 304 Not Modified
response if it matches the ETag exactly. A strong ETag implies exact
equality: the response must match byte for byte. This is necessary for
doing Range requests within a large video or
PDF file, for example, or for compatibility with some CDNs that don't
support weak ETags.

:last_modified Sets a “weak” last-update validator on the
response. Subsequent requests that set If-Modified-Since may return a 304
Not Modified response if last_modified <= If-Modified-Since.

:public By default the Cache-Control header is private, set
this to true if you want your application to be cacheable by
other devices (proxy caches).

:template By default, the template digest for the current
controller/action is included in ETags. If the action renders a different
template, you can include its digest instead. If the action doesn't
render a template at all, you can pass template: false to skip
any attempt to check for a template digest.

You can also pass an object that responds to maximum, such as
a collection of active records. In this case last_modified
will be set by calling maximum(:updated_at) on the collection
(the timestamp of the most recently updated record) and the
etag by passing the object itself.

def index
@articles = Article.all
fresh_when(@articles)
end

When passing a record or a collection, you can still set the public header:

You can use this method when you have an HTTP response that never changes,
and the browser and proxies should cache it indefinitely.

public: By default, HTTP responses are private, cached only on
the user's web browser. To allow proxies to cache the response, set
true to indicate that they can serve the cached response to
all users.

Sets the etag and/or last_modified on the
response and checks it against the client request. If the request
doesn't match the options provided, the request is considered stale and
should be generated from scratch. Otherwise, it's fresh and we
don't need to generate anything and a reply of 304 Not
Modified is sent.

Parameters:

:etag Sets a “weak” ETag validator on the response. See the
:weak_etag option.

:weak_etag Sets a “weak” ETag validator on the response.
Requests that set If-None-Match header may return a 304 Not Modified
response if it matches the ETag exactly. A weak ETag indicates semantic
equivalence, not byte-for-byte equality, so they're good for caching
HTML pages in browser caches. They can't be used for responses that
must be byte-identical, like serving Range
requests within a PDF file.

:strong_etag Sets a “strong” ETag validator on the response.
Requests that set If-None-Match header may return a 304 Not Modified
response if it matches the ETag exactly. A strong ETag implies exact
equality: the response must match byte for byte. This is necessary for
doing Range requests within a large video or
PDF file, for example, or for compatibility with some CDNs that don't
support weak ETags.

:last_modified Sets a “weak” last-update validator on the
response. Subsequent requests that set If-Modified-Since may return a 304
Not Modified response if last_modified <= If-Modified-Since.

:public By default the Cache-Control header is private, set
this to true if you want your application to be cacheable by
other devices (proxy caches).

:template By default, the template digest for the current
controller/action is included in ETags. If the action renders a different
template, you can include its digest instead. If the action doesn't
render a template at all, you can pass template: false to skip
any attempt to check for a template digest.

Example:

def show
@article = Article.find(params[:id])
if stale?(etag: @article, last_modified: @article.updated_at)
@statistics = @article.really_expensive_call
respond_to do |format|
# all the supported formats
end
end
end

You can also just pass a record. In this case last_modified
will be set by calling updated_at and etag by
passing the object itself.

def show
@article = Article.find(params[:id])
if stale?(@article)
@statistics = @article.really_expensive_call
respond_to do |format|
# all the supported formats
end
end
end

You can also pass an object that responds to maximum, such as
a collection of active records. In this case last_modified
will be set by calling +maximum(:updated_at)+ on the collection (the
timestamp of the most recently updated record) and the etag by
passing the object itself.

def index
@articles = Article.all
if stale?(@articles)
@statistics = @articles.really_expensive_call
respond_to do |format|
# all the supported formats
end
end
end

When passing a record or a collection, you can still set the public header:

def show
@article = Article.find(params[:id])
if stale?(@article, public: true)
@statistics = @article.really_expensive_call
respond_to do |format|
# all the supported formats
end
end
end

When rendering a different template than the default controller/action
style, you can indicate which digest to include in the ETag: